This one's basically a leaping-off point for ideas. This list is not exhaustive and is subject to change as people suggest new stuff.

Panel speakers on various skeptical topics

Individual presentations on various skeptical topics

Publicity, publicity, publicity!

Volunteers to help manage things at the con itself

People willing to man a table (if we get one)

Camera equipment and people to run it (so we can put all of our material on YouTube)

Audio equipment (so we can put all of our material out as podcasts)

Attention from "big name" skeptics (e.g. The Bad Astronomer, James Randi, the Skeptical Rogues from the Skeptics Guide to the Universe, The Mythbusters if we win the publicity lottery, etc. and so forth--basically anyone with some clout and some interest in spreading a skeptical message)